Tech Talk

Pavement modified, 4/10 mile track, medium banking. Rules are 2500 lbs, 58% left, 82" max width measured outside of tires. 8" tires.

Right now I'm at 57.5% left, 2550 lbs, 78" width. I've moved everything I can find to the left side of the car. I'm running 2" backspace wheels on the right, 4" backspace on the left to help the left side %.

My question is, should I go to 2" backspace on the lefts to maximize the width and give up left percentage?

Get rid of 50lbs and put 1 in backspace on all 4 corners. Move the battery to the left farther, reduce the fuel load and move the cell as far as you can to the left. Move the driver seat over as far as possible. shove the engine over as far as the mounts will let you., Move the radiator and overflow to the left, Move the firebottle to the left as far as possible. Remove anything that isn't necessary. Reduce rub rail size and wall thickness. Reduce bumper size and wall thickness.

Quote posted by student:Get rid of 50lbs and put 1 in backspace on all 4 corners. Move the battery to the left farther, reduce the fuel load and move the cell as far as you can to the left. Move the driver seat over as far as possible. shove the engine over as far as the mounts will let you., Move the radiator and overflow to the left, Move the firebottle to the left as far as possible. Remove anything that isn't necessary. Reduce rub rail size and wall thickness. Reduce bumper size and wall thickness.



if he went with 1"BS wheels on all 4 corners he would be at 82"

I've already moved the battery all the way to the left, cut off and moved the motor mounts as far left as possible, etc.

If I even up the backspacing on each side, whether 1" or 2", I will lose some left side percentage.

the question is, Is it worth losing left side percentage to go wider?

You dont need to make the track width wider. If you are that close loose the 50 lbs and leave it alone. A narrower car will get thru the corner easier, by the way...You didnt give your wheel base.

108" wheelbase. Never heard that a narrower car will get thru the corner easier. Interesting.

Quote posted by sas47:I've already moved the battery all the way to the left, cut off and moved the motor mounts as far left as possible, etc.

If I even up the backspacing on each side, whether 1" or 2", I will lose some left side percentage.

the question is, Is it worth losing left side percentage to go wider?
Definitely go with the tread width.
Rock

if narrower is better,than i guess Pontiac was wrong all these years...

Wider is better...shorter wheelbase is always better

Don't give the competition 50 pounds, 1/2% left, and 4 inches of track width. You'll have to stop, turn and accelerate 50 more pounds than the fastest car there. If you give up 1/2% left side weight, then thats additional 12 and 1/2 pounds your right side tires will have to carry that the fastest cars dont. If you give up 4 inches of track width --you'll be carrying another 30 to 35 pounds on the rights in the turns that the fastest cars don't. The fastest cars will be at 2500/58.1 left and 82 wide.

you definitely need to lose the 50lbs first, even if its on the left rail, I'd never go to the track heavy. you also need to get to the max width. Look at the competition, what are you doing differently? Start looking at your bars, too many, too heavy? body panel weights. is your fuel cell larger than you need, rad larger than you need? bellhousing, flywheels, wheels, etc, it all adds up.

First priority is to get lighter, to reach the minimum weight rule. This is most important.
Second priority is to get more left-side percentage. Is there any ballast at all on the car?
Third priority is to increase track width. Don't be surprised if a track width that is less than the 82" max gives you better maneuverability to pass someone in the middle of the turn (in a traffic situation). Also, the wider the rear axle, the more tire drag that might be created in a tight turn.
Also, don't be surprised that a narrow track-width modified on "hard" compound tires might be faster on a short run (gets more heat into the right side tires quicker, getting them up to best operating temperature).

3" lefts, 1" rights, and don't worry too much on being heavy. Tread width and left side are more important than 50 lbs. If you were 2650 it'd be a problem.

The max tread width should be your number one priority.
You should be able to get rid of some of your over weight problem your going to have to work at it very hard, but never add weight to get left side percentage.
Again,this is just me.
Rock

never be heavy to gain left side....

there is a math equation that can help. weight transfer = gforce x total weight x cg (center of gravity height) divided by tread width.....
so weight transfer = lets say 1 g for simplicity x 2550 pounds x lets say 20 inches above the ground for center of gravity height divided by lets say the tread width at 78 inches outside to outside is probably 68 inches measured at center line of the tires.-------so weight transfer = 1 x 2550 x 20 divided by 68----weight transfer = 750lbs.... now that was with a outside to outside of 78 inches-------------now plug in the same for a car with 80 inches outside to outside ------weight transfer = 1g x 2550 x 20 divided by tread with of 70 inches center line of tires ----so weight transfer is --728.5 pounds

with 78 inches----750lbs transfer---with 80 inches -----728.5 pounds transfer
with 2 inches wider tread width the car will transfer 21.5 less pounds to the right side of the car. so put you car on scales with 4 inch lefts write the weights down --then change to 2 inch lefts and see how much more weight rests on the right side tires------if it is more than 21.5 pounds stick with the 4 inch backspace---if it is less than 21.5 pounds --change to the 2 inch backspacing.......its a cheap and easy experiment as long as my math is correct. is it? anyone!

Student,
your example is good but is doesn't answer his question, the question is, is he better off to max out the tread width and give up a little left side percentage or run his car narrower and max out his left side percentage.
The bottom line is the wider the tread width the better and faster the car will turn in the corners, but that does not by any means mean you will have a fast and winning car, the whole package has to be correct to be fast, the tread width is just one tool out of many.
You could max out the left percentage and the tread width and still have a car that runs in the back, so don't get stressed out over one little thing, do the best you can with what you have and adjust from there as the season go's on, don't be afraid to try different things, nothing ventured nothing gained.
I would max out my tread width, line up the right side and go from there.
Oh ya a few post up he talked about if he has to change his camber that will change his tread width, it will change it more the way the track does it then the way you check your contact patch, because the track checks it at spindle center and that will move a lot more then the contact patch. So make sure you have room to play with on your tread width, this is way I always use a 1/8" to 1/4" wheel spacer on both fronts, that way if I have to change my camber for any reason and depending on witch way I have to go it could widen out my tread width but with the spacers I have a tool to play with.
Just an idea to think about.
Rock

Thanks for the responses. I always like an active discussion.

Just some background info. I've already done extensive rework of the car to reduce the overall weight and increase left side percentage. The 50 lbs I am over will have to be addressed through a lighter bellhousing and transmission, when funds make that an option.

I will include the information from this discussion in my setup and see how things go in pre-season testing. I'll post an update with my results.

Thanks Rock. In sas47 situation he could run 2's or 4's on the left. Depending on how much static left side weight he would lose by switching to 2's which way is better. The weight transfer formula says he'll transfer 21.5 lbs less with the 2's but give up an unknown static left side weight. If by changing to 2's the car lost 21.5 pounds left side weight the formula would say that the car would end up with the same weight on the right side tires in the corner. If weight transfer alone is not the reason for making the car wide what other reason is there? How does the wide track width make the car better and faster? Thanks so much for your help your advise has made my car so much faster.

Student, to be honest I don't think I can answer your question. But lets say you have two cars one with a 20" tread width and one with a 80" tread width which one do you think will turn better?
It's not the weight transfer your looking for, in fact you don't want any weight transfer that's the reason to have the correct shocks, sway bar, Etc.
The wider the tread width the less weight transfers around making it easier to balance the chassis and it is a must to have a balanced chassis.
The wider the car the more the weight is distributed more evenly or makes it a little easier to keep it where you want/need it.
And this is just another tool of many to help the car to stick better and turn.
There are many people on here that could do a better job at this then I can.
Again I am by no means a chassis expert, just things I have learned in my 50 years messing with race cars.
Another thing that came to me, why do you think that most of the cars that run up front go to great lengths to max out their tread width rules.
Rock

I'll run narrow if I can keep my balljoints closer to rim centers. The leftside weight rules limit in most cases but out here with 60%L to no left rules many car run -5's all four corners. Running major offsets really promotes scrub radius issues. We won last two years with 78.25" wide under 80" rules...

Your right about the scrub radius, I have always, when running a 10" wheel ran 5" backspace wheels, and max tread width, you just build the car accordingly, rear end, a-arms, etc. Why would you give up anything that enhances performance, it's a race car not a street rod.
Just a note, why do you think the track has a max tread width rule and they do not have minimum tread width rule.
Rock

Since it's a modified, can you move your suspension mounts to extend the right side and/or tuck the left sides in? If so you should be able to achieve any track width with any left %, with any wheel offset.

So if chosing between running all 4s or all 5's, 5's are better?

Pavement slm

the scrub radius is less with 5s than 4s so that is better as long as you can still get to the max width allowed by rules, and have correct camber gain and roll center for your setup and the track or tracks you race.

How does one get a 67" front track using 5s?

spacers, longer lowers?

bigspring car, so ford style lowers?